The technique of living polymerization, one of the precision polymerization techniques, enables molecular weight and molecular weight distribution controls, among others, and is utilized in producing various functionalized materials such as terminally functionalized polymers, block polymers and graft polymers. The technique of atom transfer radical polymerization, one of the living polymerization techniques, enables the polymerization of vinyl monomers selected within a wide range under mild conditions and therefore is particularly of high utility value. As an example of atom transfer radical polymerization, there may be mentioned, for example, a polymerization system in which an organic halide or halosulfonyl compound is used as the initiator and a metal complex composed of a VIII, IX, X, or XI group element in the periodic table as a central metal is used as a catalyst (cf. e.g. Patent Document 1 to 4).
The vinyl polymers produced by such methods of polymerization are characterized in that they have a halogen group at one or each polymer terminus.
Halogen group-containing vinyl polymers can be used, for example, as intermediates for the production of various functionalized materials. For example, alkenyl group-containing vinyl polymers can be produced by converting the halogen group to an alkenyl group-containing group. Alkenyl group-containing vinyl polymers, when reacted with a compound containing a plurality of hydrosilyl groups within the molecule, are crosslinked to give cured products. Further, when the alkenyl group is reacted with a reactive silyl group-containing hydrosilane compound, the reactive silyl group can be introduced into the vinyl polymers. In these reactions, the hydrosilylation reaction in which a complex of a metal such as platinum is used as a catalyst is generally utilized. Further, by converting the halogen group to a polymerizable carbon-carbon double bond-containing group, such as a (meth)acryloyl group, it also becomes possible to utilize the resulting vinyl polymers as photoinduced radical-curable or thermally induced radical-polymerizable resins or as macromonomers for grafting onto other polymers.
In this manner, halogen group-containing vinyl polymers are utilizable as intermediates for the production of various functionalized materials, among others. For their being widely useful as intermediates, however, it is necessary to purify the polymers. In the case of such vinyl polymers being intended to be utilized after conversion of the halogen group to an alkenyl group, for instance, the polymerization catalyst or the like remaining in the vinyl polymers acts as a catalyst poison in the hydrosilylation reaction and therefore, it becomes necessary to purify the polymers. The residual polymerization catalyst or the like also has a fundamental problem in that it causes marked discoloration of the vinyl polymers. Further, in cases where the halogen group is converted to a polymerizable carbon-carbon double bond-containing group, for example a (meth)acryloyl group, followed by photoinduced radical curing to give cured products, such discoloration of vinyl polymers influences the curability.
The present inventors have already developed an adsorption treatment method as a method of removing the polymerization catalyst and the like and increasing the hydrosilylation activity (cf. Patent Document 1). Such method makes it possible to efficiently remove the polymerization catalyst and the like to thereby increase the hydrosilylation activity and inhibit the resins from being discolored.
Various methods based on the principle of adsorption treatment are known as methods for efficiently removing polymerization catalysts. According to Patent Document 2, the polymerization catalyst is efficiently removed to a residual metal content level of several hundred ppm by a method comprising the step of heating at a temperature not lower than 50° C. but not higher than 250° C. in the presence of a solid additive at a low solid addition level, followed by solid-liquid separation.
Patent Document 3 describes the effect of treatment with an oxidizing agent such as oxygen in the step of heating. It is stated that the residual metal is removed to a residual level of several hundred ppm to several tens of ppm and the curable hydrosilylation product obtained in the subsequent step is thereby improved in curability. Further, mention is made of the polarity of the solvent to be used in removing the residual metal and, according to it, the relative dielectric constant thereof is desirably not higher than 5; it is described that the effect of eliminating the residual metal by means of a poor solvent exerts an influence on the separability of the residual metal in the subsequent step of separation.
However, even these methods cannot remove the polymerization catalyst completely; hence, only after a plurality of repetitions of the same step, a polymer with a residual metal content causing no problem can be obtained. Those methods which are in common use for separating the polymerization catalyst comprise a solid-liquid separation procedure, such as centrifugation or filtration. Polymer losses are, however, inevitable before and after these separation procedures and, therefore, a plurality of repetitions of the separation step mean decreases in polymer yield. They also have a basic problem in that the increase in the number of steps is unfavorable from the production equipment viewpoint.
On the other hand, it is necessary to subject halogen group-containing vinyl polymers to various molecular terminus conversions so that the functions as functionalized materials may be performed. In preparing functionalized materials capable of being cured in the manner of hydrosilylation reaction, the halogen group is converted to an alkenyl group, and the terminus is then converted to a silyl terminus by the hydrosilylation reaction. In preparing radical-curable types, mention may be made of the method comprising converting the halogen group to a (meth)acryloyl group, for instance. For these terminal conversion reactions, such elementary steps as addition of a functionalizing agent and a solvent, the functionalization reaction, and separation/removal of the excess functionalizing agent are required. In case the desired functional terminus cannot be obtained in one operation, such terminal conversion reaction is repeated a plurality of times.
When these terminal conversion reactions are carried out, there arises a problem; namely, the residual polymerization catalyst in the polymer may inhibit the conversion reactions or, if it does not inhibit the reactions, it may cause discoloration of the polymer. In the case of the hydrosilylation reaction, for instance, it is known that acids, bases and various metals markedly inhibit the reactivity. Known as a method of introducing a (meth) acryloyl group is, for example, the reaction involving the addition of potassium acrylate or potassium methacrylate using N,N-dimethylacetamide as a solvent (cf. Patent Document 4 and 5). This reaction has a problem in that the residual polymerization catalyst in the polymer, if any, causes marked discoloration of the polymer. Further, when the polymer is subjected to warming treatment in the operation for removing the functionalizing agent and solvent, the discoloration of the polymer is further promoted thereby.
Therefore, it can be understood that it is very important, from the quality insurance viewpoint, to remove polymerization catalysts as far as possible prior to carrying out any terminal conversion reaction. The methods of removing polymerization catalysts as described in the above-cited Patent Documents 2 and 3 require a plurality of repetitions of these steps and, in the functional group introduction reaction for introducing a (meth)acryloyl group, in particular, they have a problem in that even very low levels of a polymerization catalyst, if remaining, cause polymer discoloration. Thus, a more efficient method of removing polymerization catalysts has been desired.
Side by side the effect of a solid additive, the effect of oxygen or an oxidizing agent in efficiently removing polymerization catalysts may be mentioned. Patent Document 6 refers to the effect of the addition of an oxidizing agent. Thus, a polymer is diluted with toluene and subjected to various oxidizing agent treatments. In the case of contacting with air, which is easiest to handle and does not need removal of any oxidizing agent, toluene was added in an amount of 9 volumes per volume of polymer and the mixture was stirred at room temperature for 8 hours while it was bubbled with air. The result was such that the residual Cu concentration after treatment was not higher than 10 ppm. Another example characterized by contacting with air at room temperature is seen in Patent Document 7. These documents mention only the possibility of small laboratory size operations and a problem will be encountered in practicing such methods on a commercial scale. Namely, it is a problem from the maintenance of safety viewpoint to bring such a system containing toluene, namely a combustible solvent having a flash point, into contact with air having an oxygen concentration of 21%. Further, these aromatic solvents such as toluene are selected in view of their effect of insolubilizing the polymerization catalyst which is a transition metal complex. For this effect, low-polarity solvents are said to be desirable. These examples refer to the effect of an oxidizing agent or oxygen in the stage after dilution with toluene.
It has been revealed, however, that the effect of an oxidizing agent or oxygen in the presence of a low-polarity solvent such as toluene is insufficient in some instances, as described later herein in a comparative example, among others. It is a further problem that the treatment with oxygen in the presence of such a low-polarity solvent as toluene is insufficient to completely remove polymerization catalysts, which are transition metal complexes; therefore, the subsequent solvent evaporation and functional group introduction procedures are carried out in the presence of residues of the polymerization catalysts, so that the final products are markedly discolored, for instance.
Patent Document 1: Japanese Kokai Publication Hei-11-193307
Patent Document 2: Japanese Kokai Publication 2004-149563
Patent Document 3: Japanese Kokai Publication 2003-327620
Patent Document 4: Japanese Kokai Publication 2000-072815
Patent Document 5: Japanese Kokai Publication 2000-072816
Patent Document 6: Japanese Kokai Publication 2002-69121
Patent Document 7: Japanese Kohyo Publication 2004-500448
Non-Patent Document 1: Matyjaszewski, et al., J. Am. Chem. Soc., 1995, vol. 117, p. 5614
Non-Patent Document 2: Matyjaszewski, et al., Macromolecules, 1995, vol. 28, p. 7901
Non-Patent Document 3: Matyjaszewski, et al., Science, 1996, vol. 272, p. 866
Non-Patent Document 4: Sawamoto, et al., Macromolecules, 1995, vol. 28, p. 1721